BEIRUT -- U.S.-backed Syrian forces entered Saturday an eastern village held by the Islamic State group where intense clashes are ongoing a day after the extremists reportedly killed 20 fighters, the forces and a war monitor said.

The Kurdish-led Syrian Democratic Forces said its fighters stormed Bagouz and are close to the centre of the village. The forces added that they plan to open another front in the Sousseh area along the Euphrates river to increase pressure on the extremists.

SDF launched with the help of the U.S.-led coalition a wide offensive this week to capture the last pocket held by IS in Syria. The Kurdish-led forces have been among the most effective in the fight against IS in Syria, forcing them out of much of the country's east.

Despite losing most of the territory it held between Iraq and Syria since its peak in 2014, the jihadist IS remains a disruptive force in both countries. Its leader, Abu Bakr al-Baghdadi, urged his followers to "persevere" in an audio tape attributed to him last month.

The IS-linked Aamaq news agency said the group's gunmen targeted advancing SDF fighters in the Bagouz area with mortar rounds, roadside bombs and sniper fire inflicting many casualties among them.

The SDF commander of the operation in Bagouz, who identified himself as Shergo, said in a video statement that the fighting is intense from both sides and that his fighters now control almost half of the village.

"We will take all this place from ISIS," Shergo said in English, using a different acronym to refer to IS.

The Britain-based Syrian Observatory for Human Rights said IS fighters are relying on a network of tunnels in the area and land mines to slow down SDF's offensive. It said that some 100 women and 30 men, including IS fighters, along with their children, surrendered to SDF fighters. The IS gunmen were taken to a tightly secured positions in the area, it added.

The storming of Bagouz came a day after the Observatory and a Kurdish official said IS gunmen killed 20 SDF fighters in the country's east.

The Observatory said the extremists took advantage of a sand storm to launch a counterattack, which killed 20 fighters and wounded others.

Kurdish official Ebrahim Ebrahim said the 20 fighters were killed in an ambush by IS fighters.

SDF said in a statement that only two of its fighters were killed and six others wounded in Friday's clashes.

The Observatory said Saturday that since SDF launched its offensive on the IS-held pocket, including the town of Hajin, 53 extremists have been killed as well as 38 U.S.-backed fighters.

The Observatory said SDF brought in Friday some 1,000 fighters to fortify its positions and boost the forces carrying out the offensive.

Photos

In this July 27, 2017 file photo, a U.S.-backed Syrian Democratic Forces fighter runs in front of a damaged building as he crosses a street on the front line, in Raqqa, Syria. (AP Photo / Hussein Malla, File)